THE PHYSIOLOGICAL CONTROL OF WATER INGESTION IN THE BLOWFLY

Abstract

The initiation, main-tenance, and termination of water ingestion by the blowfly Phormia regina Meigen is controlled by sensory input from tarsal and labellar chemoreceptive hairs. Responsiveness to water increases as a fly is desiccated and decreases as it is humidified. Injection of water, hypertonic saline or glucose, or mineral oil into the haemocoele of thirsty flies rendered them unresponsive to water. Bleeding non-thirsty flies made them thirsty. It is concluded that blood volume or pressure regulates water responsiveness. Cutting the recurrent nerve causes polydypsia. As thirst increases flies will drink ever increasing concentrations of salt when it is the only source of water; however, the greater the salt concentration the smaller the volume drunk. Starvation does not increase water ingestion. The control of water ingestion is independent of the control of sugar ingestion. It is concluded that water and sugar do not act on the same sensory neuron.